An electric train configured to collect AC power from an overhead line via a pantograph to travel is generally provided with a power converter that converts the AC power collected from the overhead line as appropriate and supplies the resulting power to a motor for traveling. In a method for controlling this type of power converter, it is common to control the device so that a power factor of the AC power inputted from the pantograph becomes unity, that is, only active power is consumed in the electric train, from a viewpoint of weight reduction and downsizing of the device.
However, controlling the power converter so that the power factor becomes unity as described above may cause the following problem. That is, along with the consumption of active power by train traveling, an overhead line voltage decreases or fluctuates due to influence of an impedance of a power source side of a feeding circuit that supplies the AC power to the overhead line, an impedance of the feeding circuit and the like. Specifically, in an electric train, like the existing Shinkansen bullet train, for example, that is designed to consume a specified active power regardless of a value of an AC voltage received from the overhead line, electric current consumed by the electric train increases as an overhead line voltage decreases. Due to the influence, the overhead line voltage may further decrease, and, in some cases, a given propulsive force may not be obtained.
As a countermeasure against the above problem caused by unity power factor control in the electric train, there is a method of maintaining the overhead line voltage equal to or higher than a standard voltage by installing a var compensator or a fixed power factor output power converter in a feeding substation. However, this method requires significant cost and a large installation space for installation of each device.
In contrast, Patent Document 1 below discloses a technique of controlling a VVVF converter so as to generate leading reactive power without setting unity power factor during power running in the electric train.
Also, Patent Document 2 below discloses a power converter that suppresses voltage fluctuation of an AC system which supplies electric power to a vehicle on the AC system side. That is, Patent Document 2 discloses a technique of suppressing voltage fluctuation of the AC system by autonomously determining an active power consumption and a reactive power consumption based on an AC system voltage, and coupling to the AC system the power converter that simultaneously consume the determined active power and reactive power.